// Copyright (c) 2021, gottingen group.
// All rights reserved.
// Created by liyinbin lijippy@163.com

//
// abel::base_internal::Invoke(f, args...) is an implementation of
// INVOKE(f, args...) from section [func.require] of the C++ standard.
//
// [func.require]
// Define INVOKE (f, t1, t2, ..., tN) as follows:
// 1. (t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class T
//    and t1 is an object of type T or a reference to an object of type T or a
//    reference to an object of a type derived from T;
// 2. ((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a
//    class T and t1 is not one of the types described in the previous item;
// 3. t1.*f when N == 1 and f is a pointer to member data of a class T and t1 is
//    an object of type T or a reference to an object of type T or a reference
//    to an object of a type derived from T;
// 4. (*t1).*f when N == 1 and f is a pointer to member data of a class T and t1
//    is not one of the types described in the previous item;
// 5. f(t1, t2, ..., tN) in all other cases.
//
// The implementation is SFINAE-friendly: substitution failure within Invoke()
// isn't an error.

#ifndef ABEL_FUNCTIONAL_INTERNAL_INVOKE_H_
#define ABEL_FUNCTIONAL_INTERNAL_INVOKE_H_

#include <algorithm>
#include <type_traits>
#include <utility>

#include "abel/meta/type_traits.h"

// The following code is internal implementation detail.  See the comment at the
// top of this file for the API documentation.

namespace abel {

namespace base_internal {

// The five classes below each implement one of the clauses from the definition
// of INVOKE. The inner class template Accept<F, Args...> checks whether the
// clause is applicable; static function template Invoke(f, args...) does the
// invocation.
//
// By separating the clause selection logic from invocation we make sure that
// Invoke() does exactly what the standard says.

template<typename Derived>
struct StrippedAccept {
    template<typename... Args>
    struct Accept : Derived::template AcceptImpl<typename std::remove_cv<
            typename std::remove_reference<Args>::type>::type...> {
    };
};

// (t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class T
// and t1 is an object of type T or a reference to an object of type T or a
// reference to an object of a type derived from T.
struct MemFunAndRef : StrippedAccept<MemFunAndRef> {
    template<typename... Args>
    struct AcceptImpl : std::false_type {
    };

    template<typename MemFunType, typename C, typename Obj, typename... Args>
    struct AcceptImpl<MemFunType C::*, Obj, Args...>
            : std::integral_constant<bool, std::is_base_of<C, Obj>::value &&
                                           abel::is_function<MemFunType>::value> {
    };

    template<typename MemFun, typename Obj, typename... Args>
    static decltype((std::declval<Obj>().*
                     std::declval<MemFun>())(std::declval<Args>()...))
    Invoke(MemFun &&mem_fun, Obj &&obj, Args &&... args) {
        return (std::forward<Obj>(obj).*
                std::forward<MemFun>(mem_fun))(std::forward<Args>(args)...);
    }
};

// ((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a
// class T and t1 is not one of the types described in the previous item.
struct MemFunAndPtr : StrippedAccept<MemFunAndPtr> {
    template<typename... Args>
    struct AcceptImpl : std::false_type {
    };

    template<typename MemFunType, typename C, typename Ptr, typename... Args>
    struct AcceptImpl<MemFunType C::*, Ptr, Args...>
            : std::integral_constant<bool, !std::is_base_of<C, Ptr>::value &&
                                           abel::is_function<MemFunType>::value> {
    };

    template<typename MemFun, typename Ptr, typename... Args>
    static decltype(((*std::declval<Ptr>()).*
                     std::declval<MemFun>())(std::declval<Args>()...))
    Invoke(MemFun &&mem_fun, Ptr &&ptr, Args &&... args) {
        return ((*std::forward<Ptr>(ptr)).*
                std::forward<MemFun>(mem_fun))(std::forward<Args>(args)...);
    }
};

// t1.*f when N == 1 and f is a pointer to member data of a class T and t1 is
// an object of type T or a reference to an object of type T or a reference
// to an object of a type derived from T.
struct DataMemAndRef : StrippedAccept<DataMemAndRef> {
    template<typename... Args>
    struct AcceptImpl : std::false_type {
    };

    template<typename R, typename C, typename Obj>
    struct AcceptImpl<R C::*, Obj>
            : std::integral_constant<bool, std::is_base_of<C, Obj>::value &&
                                           !abel::is_function<R>::value> {
    };

    template<typename DataMem, typename Ref>
    static decltype(std::declval<Ref>().*std::declval<DataMem>()) Invoke(
            DataMem &&data_mem, Ref &&ref) {
        return std::forward<Ref>(ref).*std::forward<DataMem>(data_mem);
    }
};

// (*t1).*f when N == 1 and f is a pointer to member data of a class T and t1
// is not one of the types described in the previous item.
struct DataMemAndPtr : StrippedAccept<DataMemAndPtr> {
    template<typename... Args>
    struct AcceptImpl : std::false_type {
    };

    template<typename R, typename C, typename Ptr>
    struct AcceptImpl<R C::*, Ptr>
            : std::integral_constant<bool, !std::is_base_of<C, Ptr>::value &&
                                           !abel::is_function<R>::value> {
    };

    template<typename DataMem, typename Ptr>
    static decltype((*std::declval<Ptr>()).*std::declval<DataMem>()) Invoke(
            DataMem &&data_mem, Ptr &&ptr) {
        return (*std::forward<Ptr>(ptr)).*std::forward<DataMem>(data_mem);
    }
};

// f(t1, t2, ..., tN) in all other cases.
struct Callable {
    // Callable doesn't have Accept because it's the last clause that gets picked
    // when none of the previous clauses are applicable.
    template<typename F, typename... Args>
    static decltype(std::declval<F>()(std::declval<Args>()...)) Invoke(
            F &&f, Args &&... args) {
        return std::forward<F>(f)(std::forward<Args>(args)...);
    }
};

// Resolves to the first matching clause.
template<typename... Args>
struct invoker {
    typedef typename std::conditional<
            MemFunAndRef::Accept<Args...>::value, MemFunAndRef,
            typename std::conditional<
                    MemFunAndPtr::Accept<Args...>::value, MemFunAndPtr,
                    typename std::conditional<
                            DataMemAndRef::Accept<Args...>::value, DataMemAndRef,
                            typename std::conditional<DataMemAndPtr::Accept<Args...>::value,
                                    DataMemAndPtr, Callable>::type>::type>::
            type>::type type;
};

// The result type of Invoke<F, Args...>.
template<typename F, typename... Args>
using InvokeT = decltype(invoker<F, Args...>::type::Invoke(
        std::declval<F>(), std::declval<Args>()...));

// Invoke(f, args...) is an implementation of INVOKE(f, args...) from section
// [func.require] of the C++ standard.
template<typename F, typename... Args>
InvokeT<F, Args...> Invoke(F &&f, Args &&... args) {
    return invoker<F, Args...>::type::Invoke(std::forward<F>(f),
                                             std::forward<Args>(args)...);
}
}  // namespace base_internal

}  // namespace abel
#endif  // ABEL_FUNCTIONAL_INTERNAL_INVOKE_H_
